The present invention relates to a self-orientatable twin wheel of the kind comprising a pair of coaxial wheels.
So-called twin wheels are constituted by a pair of wheels rotatably mounted on a pivot. Said pviot is horizontally supported by a support which comprises a vertical wall, which extends between the wheels and is arranged in a perpendicular plane, and a sort of semi-cylindrical housing which upwardly covers the wheel. A sort of well is provided in said vertical wall which is open upward and acts as a rotation seat for a vertical self-orientation pivot intended to be inserted and fixed in a seat of the piece of furniture to which the wheel is to be applied.
Two tubular portions extend from both faces of the wall which are coaxial to the pivot and are internally provided with coupling elements for a collar which is externally provided on a hollow tang which is rigidly associated with the respective wheel. Said tang acts in practice as a bearing for the rotatable support of the wheel on the pivot.
Conventional twin wheels have substantial disadvantages related to the manufacturing method which comprise their adaptation to the "standards" set by safety rules. In particular, in order to increase wear resistance, it is known to manufacture the wheels entirely in polyamide resins, whereas copolymers (e.g. polypropylene loaded with rubber), which have greater elasticity characteristics, are usually adopted if greater shock-resistance is to be achieved.
In any case, wheels made of polyamide resins have an excessive cost due to the high cost of this material.
Polyamide resins are furthermore very hard, so that the wheels are excessively noisy in rolling.
The German utility model No. 74 32 250 discloses a wheel provided with a supporting bush on the pivot.
Said bush has no means which allow its retention on said pivot, so it is necessary to resort to an additional elastic ring which makes assembly more laborious.
The UK patent No. 1 299 583 discloses a wheel with a pivot which is rotatably supported in a bush made of plastic material and provided with means which allow to retain it on the pivot. However, in order to incorporate the retention means in the bush, since undercuts are involved, it is necessary to provide the bush in two specularly identical parts which tend to deform under load, thereby compromising the rotation of the pivot.